A cutting tool for machining a work material made of metal or the like includes a holder and a cutting insert mounted to the holder.
For example, a cutting insert disclosed in Japanese Unexamined Patent Application Publication No. 2008-73827A includes a corner cutting edge that is disposed at an intersection between a top surface and side surfaces and positioned at a corner section between a first side and a second side of the top surface, and a rake face positioned along a cutting edge on the top surface. Furthermore, this cutting insert includes a protruding section near the corner cutting edge of the top surface.
Further, in a direction orthogonal to a bisecting line of the corner section, a width of a tip portion of the corner cutting edge side of this protruding section is small compared to a width of the corner cutting edge.
A protruding section such as described above is disposed near the corner cutting edge, making it possible to make chips, which have been cut by the corner cutting edge when cutting a work material using the corner cutting edge and a first cutting edge, come into contact with the protruding section to change a direction of movement of the chips. As a result, it is possible to facilitate the generation of curled chips.
Nevertheless, according to such a cutting insert as described above, under cutting conditions of a small depth of cut such as when a feed rate is decreased and only the corner cutting edge is used, the following problem arises. That is, the feed rate is decreased, thereby decreasing a thickness of the chips, which potentially leads to an unstable chip discharge direction. Further, the depth of cut is decreased, thereby increasing the likelihood that the chips will come into contact with a tip portion of the protruding section, which is small compared to a width of the corner cutting edge. As a result, the problem arises that the direction of movement of the curled chips is not stabilized, potentially leading to unstable chip generation.